Certain types of cancerous tumors, such as breast cancer tumors, particularly inflammatory and locally advanced tumors, often resist traditional treatments. It has been statistically shown that sixty to seventy percent of victims of such breast tumors do not survive past five years. The efficacy of conventional methods of treating cancer, such as radiotherapy and chemotherapy, is limited due to necessary constraints on dosage amounts for safety.
For example, it is known that chemotherapy can be applied in sufficient amounts to kill virtually all cancer cells of a tumor. However, the amounts of chemotherapy needed to achieve this can be high enough to cause poisoning of the patient and/or undue side effects. As another example, the intensity of an x-ray beam applied in accordance with radiotherapy cannot be set at an intensity that will damage nearby critical organs and surrounding healthy tissues. Accordingly, there is an ongoing need to develop techniques that enhance existing cancer-related therapeutic procedures so as to increase their effectiveness without increasing the risk of damage to healthy tissue and causing additional discomfort for cancer patients, and also for developing new methods of cancer treatments.
It has been found that the effectiveness of radiation therapy and chemotherapy can be increased by heating a tumor or other cancer tissue immediately before, during, or immediately after the application of radiation in radiation therapy or the application of cancer treating chemicals in chemotherapy. This increased effectiveness can reduce the amount of radiation or chemicals needed for successful radiation therapy or chemotherapy thereby making radiation therapy or chemotherapy available to patients who might not be able to tolerate such treatment otherwise. When heating is combined with radiation therapy or chemotherapy, it is desirable to maintain the temperature of the treated diseased tissue within the range of about 42 to 45 degrees C. Treatment within this controlled temperature range is usually referred to as hyperthermia.
Forms of thermal therapy that kill diseased tissue with heating alone are generally referred to as coagulation or ablation. To adequately eradicate a cancerous tumor with only the application of heat, it is generally necessary to heat the diseased tissue to at least about 55 degrees C., and typically above about 60 degrees C., for exposure times sufficient to kill the cells, typically for greater than about one minute. With such coagulation or ablation treatments, it is important to sufficiently heat the diseased tissue to be treated but to limit heating of the normal tissue surrounding the diseased tissue.
Breast tumors that have grown to a size of about 3 cm to about 5 cm are particularly hard to treat and are hard to remove surgically, generally requiring removal of the breast to remove the tumor. Alternative treatments for such tumors are needed.
One recent approach toward improving cancer therapy is to subject a tumor to a hyperthermia treatment, i.e., heating of the tumor. As indicated, the application of heat to cancer cells has been found to increase the efficacy of certain types of therapies for various proposed reasons. Microwave and radio frequency (RF) energy sources have been employed to conduct hyperthermia treatment. Microwave energy has been applied to tumors using waveguides. However, the relatively high frequencies at which microwaves propagate are generally not suitable for deep penetration into tissue.
RF energy at a lower frequency has also been utilized in some instances, and has the potential to achieve greater penetration due to its relatively lower frequencies. However, both microwave and RF techniques have typically used invasive elements, such as wires, catheters, lumens, probes, receivers, and the like. These invasive elements are usually inserted or embedded in the tumor to be treated to ensure proper coupling and focusing of the electromagnetic energy at the tumor site. The use of invasive elements adds complexity to the procedure and is a source of discomfort for patients. Examples of invasive heating techniques using microwave and RF energy are disclosed in U.S. Pat. Nos. 5,928,159; 6,275,738; 6,358,246; 6,391,026; 5,540,737, and 6,468,273.
One prior method for hyperthermia treatment involves the use of phased arrays of dipoles surrounding portions of a body in which a selected portion, such as a tumor, is desired to be heated. The dipoles are operated in a coherent phase or at least a synchronous phase relationship to enable selective targeting of deep tissue tumor masses by controlling the power and relative phase applied to the array of dipoles. These dipoles couple their RF or microwave energy to the body through typically deionized water media as it is high in dielectric constant similar to most of the body tissues but is lower in electrical conductivity so it provides small wavelengths but low power absorption. The antenna arrays surrounding such tissue structures have generally been in concentric arrays using lower frequencies with long wavelengths or have been at high frequencies, at or near microwave frequencies, but not in arrangements that would produce selective resonant behavior in tumors of the breast nor create circular polarization that would improve uniformity of such tissue target heating.
Samulski, in U.S. Pat. No. 6,904,323, described the use of phased array dipoles that are placed around a cavity containing fluid such as water and where a human breast containing a cancerous tumor can be submerged and heated by the surrounding dipole antennas. This method uses rather low frequencies that produce a very large wavelength in both high water tissues of the body and in low water content tissues such as mammary fat. The operation, typically at a frequency of about 140 MHz, results in a wavelength in fatty tissue of about 86 cm and in muscle tissues of about 22.9 cm.
There remains a need for an improved method and apparatus for more selectively inducing hyperthermia in tumors and malignant tissue or for otherwise providing selective heating of tissue in need of hyperthermia or other heat treatment, particularly for such tissue that reside within a breast or other portion of a body where such tumor is surrounded by fatty low water tissue, while avoiding or at least decreasing the potential of excessively heating the surrounding tissue.